At the present time, various mobile scaffold units are in common use. Typically, these units include a framework made of structural tubing, with four vertical columns at the four corners of the unit, various horizontal and diagonal cross braces, and an elevated work platform supported on the framework. Typically, such scaffolds may be of single or double width, the single width being small enough so that the scaffold unit may be moved through standard 30-inch doorways, and the double width providing more platform area. Such scaffold units come in various standard lengths, such as six, eight or 10 feet. Such scaffold units have casters mounted on the lower end of the four corner columns to enable the scaffold units to be rolled from place to place. Usually, each caster includes an adjustable leg enabling the height of each column to be adjusted relative to the floor on which the caster rests. Such adjustment will typically enable the work platform to be adjusted by up to about 12 inches.
In normal use by one workman, the workman will roll the scaffold unit to a place where work is to be done, and he will then climb up to the scaffold platform to perform the work. If it is then desired to move the scaffold a short distance to a new position so that the work may be continued, the workman must climb down to the floor, roll the scaffold to the new position and remount the scaffold to continue the job.
There are times when it would be desirable to have such a scaffold equipped with a propulsion unit so that the workman could move and steer the scaffold to a new location without demounting from the elevated platform.
There are several problems in providing a suitable power drive for such a scaffold unit.
A first problem is that the tubing framework of most movable scaffolds is relatively lightweight and the castered columns are not designed to withstand the relatively high lateral forces that could be imposed on the unit when it is power driven.
Another problem is that such a scaffold unit with a workman on the platform will have a relatively high center of gravity and a consequent reduction in low degree of stability when subjected to lateral forces.
A still further problem is that it is desirable that the scaffold unit, when power driven, be able to go over relatively small obstacles, such as a piece of plasterboard, but not to be able to go over obstacles of such thickness as may cause an excessive degree of tilting of the scaffold.
In addition, it is desirable that a propulsion unit for such a scaffold provide for easy maneuvering of the scaffold, and that it be easily and quickly attached to or detached from the scaffold.
Further, it is desirable that the scaffold be easily and manually moved by a workman on the ground when the propulsion unit is attached to the scaffold.
It is the object of the present invention to overcome one or more of the above problems and to meet one or more of the above desires.